OK: Ring and pinion. They are a mated set and can never be used 1 with out the other one. They are never replaced 1 at a time. Always as a set. Otherwise they will self destruct.
The drop out. That is the part you see bolted to the differential housing and holds everything in place.

Carrier. That is the part that holds the differential gears and ring & pinion.

Spider gears, AKA the differential. That is why when you turn one wheel one direction the other one goes the other way. With out it you will have axle bind when turning a corner. When going around the corner the outside tire must travel further then the inner one.

Pumpkin. The bulge in the rear housing.
I hope this helps. But You can find more on the workings in the manual section, under UTI training manuals. It's good info to scan through.